MTA Sets New Tactic In Rat War

Locked in endless struggle with the rodents that infest the subway, transit officials have tried poison and deadly traps. They've blocked rat-size pathways into tempting trash rooms and removed garbage cans from station platforms.

Now, they're ready to try birth control.

Working with SenesTech Inc., the Metropolitan Transportation Authority is launching the first urban trial of a pest-control bait that induces permanent infertility in rats. The product has succeeded in rural environments, lowering rodent populations without harming other animals, crops or humans.

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Rat peeking out of a hole at an F train stop in Brooklyn.
Julie Jacobson/Associated Press

In New York, however, the company faces a new and vexing challenge: Big-city rodents have developed more sophisticated palates than their country counterparts, who have been lured into switching from grains or other foods to the bait.

"Rats in Laos, they like coconut. But the rats in Indonesia prefer fish flavor," Loretta Mayer, co-founder of Arizona-based SenesTech, said of the regional variation in rat appetites. "You have to be very much one with the animal."

But winning over rattus Norvegicus, the species common to New York, means making bait that's more alluring than the pizza crusts, discarded Chinese takeout and cold French fries littering the subway system. It is a difficulty the company acknowledged in a grant application to the National Institutes of Health, which has put up more than $1 million to finance tests of its sterilizing product, ContraPest, in a metropolitan setting.

Existing baits, the company wrote, are hampered in cities by "the abundance of more palatable food choices (i.e. trash)."

Later this month, Dr. Mayer and her colleagues will launch a rodent taste test in a handful of subway trash rooms. The scientists will spread birth-control bait of different flavors and scents. Should other available food scraps prove too tantalizing, Dr. Mayer didn't rule out resorting to using pieces of pepperoni.

"We really won't know [what works] until we get in there," she said.

In one area of the subway, SenesTech specialists might try a version of the birth-control bait that mimics the smell of a snack that Robert Corrigan, a renowned rodentologist and adviser to the city, has used in his own traps: chicken nuggets.

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Rattus Norvegicus

Dr. Corrigan has seen the resilience of New York City rats in the face of conventional poison schemes. Females start breeding at four months old and give birth to litters of a half-dozen offspring about four times per year, he said, meaning any poison has to outpace reproduction.

Dead rats don't necessarily mean fewer rats in the long run, said Thomas Lamb, chief of innovation and technology for New York City Transit. By lowering the competition for food, successful poisons tend to make the survivors more healthy and fertile, leading to a rapid rebound in the pest population.

Rats eventually outsmart even the best poisons. "It doesn't take them long to figure out, 'Hey, Uncle Charlie croaked after eating that,'" Mr. Lamb said.

"We basically bait, trap and kill," he said of the status quo. "If we just continue to do that, every year we'll have the same expense and the same result."

"It's a very natural thing," she said. "We're just accelerating it in these animals."

The product metabolizes into inactive compounds within hours of being ingested, she said, a feature crucial to its development for use in rice fields in Asia, where farmers needed something that wouldn't sicken other animals and children. The chemical won't leach into water or climb back up the food chain to affect other species.

The goal, Dr. Mayer said, isn't Rat Zero: "Our product is not designed to eradicate any species. That's a human error that needs to not be repeated."

The bait contains dye, which will be measured in a black-light examination of rat whiskers to reveal how quickly subway critters consume the ContraPest and whether a change to a more flavorful recipe might be needed.

"They'll either have to change the ingredients or put it out with a hamburger or whatever the heck the rats are eating," Mr. Lamb said.

Picking the most effective flavor and scent for the bait depends in large part on the specific rats, Dr. Corrigan explained in an email. If subway rats have grown up eating from the trash bags and track litter of the subway system, those foods will prove most enticing.

It's nurture as much as nature: "Rats that grow up, say, from the dumpster behind a fast food chicken place, will love chicken," Dr. Corrigan said. "Bagel place, bagels. And so on."

If the SenesTech taste test proves successful and birth-control bait is used throughout the transit system, the average life span of subway rats—which now tops out at about one year, according to Mr. Lamb—would probably rise slightly even as the total population declines.

Indeed, Mr. Lamb said the MTA's goal is to carefully manage a smaller rat population that is less likely to make shriek-inducing treks across subway stations in search of sustenance.

Keeping some rats around is actually a little useful. "They do eat cockroaches and things like that," Mr. Lamb said.

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